Electrical musical instrument



lNru 7 June 10, 1941.. M 1 2,245,354

ELECTRICAL MUSICAL INSTRUMENT Filed Dec. 8, 1938 2 Sheets-Sheet 2 IPatented June 10, 1941 UNITED STATES PATENT I OFFICE v I 2,245,354EIECTBICAI. MUSICAL INSTRUMENT Matthew 2. Mrol, Chicago, 111., assignorto Hammond Instrument Company, Chicago, 111., a corporation of Delaware4 Application December 8,1938, Serial No. 244,555

6 Claims. (Cl. 84-135) My invention relates generally to electricalmusical instruments, and more particularly to improved apparatus forproducing tremulant effects for such instruments.

Various types of apparatus have been utilized to produce a tremulanteilect in the output of electrical musical instruments. Generally, suchvention, the tremulant effect is obtained in a novel manner whereby theamplitude modulation of the signal is not uniform throughout thefrequency range of the instrument, but instead, takes place in suchmanner that the amplitude of one frequency may be increasing, while thatof another frequency is decreasing. Stated in another way, the amplitudemodulations of differentfrequencies are out of phase. This type oftremulant causes a continuous variation in the relative amplitudes ofthe'component frequencies so that the musical efl'ect approaches that ofa description, reference being had to the accompanying drawings inwhich:

- Figure 1 shows several instantaneous frequency response curves of theapparatus at different I points in the tremulant cycle; and,

Figure 2 is a wiring diagram showing an exemplary form of apparatus orcircuit which may be used to perform the method and accomplish theobjects of the invention.

In electrical musical instruments such as the electric organ shown inthe patent to Laurens vibrato, i. e., a periodic :change in pitch, moreclosely than that of acustomary tremulant.

It is thus an object of my invention to provide an improved tremulantcircuit and apparatus for electrical musical instruments. in which theamplitude modulations ofthe different component frequencies of a signalare appreciably out of phase.

A further object is to provide a tremulant apparatus for electricalmusical instruments capable of producing a signal containing a pluralityof frequencies, which is'periodically effective to cause some of thefrequencies to increase in amplitude while causing other frequencies todecrease in amplitude.

. ,A further object is to provide a tremulant apparatus for electricalmusical instruments in which the effectiveness of the amplitudemodulation is non-uniform throughout the frequency range of theinstrument.

A further object is to provide an improved method of producing atremulant effect in the output of electricalv musical instruments.

Other objects will appear. from the following Hammond, No. 1,956,350,granted April 24, 1984, the output circuit is designed to attenuate thehigh frequencies to a greater extent than the lower frequencies, forreasons fully described in said patent. The nature of the frequencyresponsive curve of the output circuit of such an organ is representedby the full line curve A' of Figure 1. An ordinary tremulant apparatusor circuit in which the impedance of the output circult is periodicallyvaried, as by a cyclically variable resistance or potentiometer, doesnot cause any appreciable change in the general shape of this curve A,but merely causes it to be translated vertically, i. e., all of thedifferent .frequencies are similarly affected and all are increasing inamplitude during approximately one-half of the cycle, and decreasing inamplitude during the remaining portion of the tremulant cycle.

In accordance with the principle of my invention, the general shape ofthe response curveis being continuously changed by the tremulantapparatus so that the effect of the tremulant differs with the frequencyof the signal. The variation is of such character that of two diflerentfrequencies included in the signal, the tremulant apparatus may causeamplitude modulation of one frequency in an increasing direction, whileat the same time, another frequency is decreasing in amplitude, and viceversa. This effect is illustrated in Figure 1, wherein the dash-linecurve B represents the response of the apparatus at one instant duringthe tremulant cycle, while the dotted line curve C represents theresponse of the output circuit at another instant of the tremulantcycle. The response curves of :the output circuit at instantsintermediate those represented by -the curves B and C may lieintermediate the curves B and C, or may be of such shape as to cross thecurves B or C, or both, at

one or more points.

An examination of Figure 1 discloses that between the intervalrepresented by the nves B and C, frequencies below 200 cycles are, onthe average, progressively increasing in amplitude;,

frequencies from about.200 to approximately 500 cycles are, in general,decreasing in amplitude; and frequencies above 500 cycles are generallyincreasing in amplitude. Y

The curves B and G are merely illustrative of the response-curves which-'.maybe-obtained by any suitable m'esh placed in the output circuit ofthe instrument in which one or more of the impedances are periodicallyvaried at a tremulant ,rate. In fact, the -curves-B and Care'rep'resentative of the response which may be obtained by arelatively simple network including the variable impedance. If a morecomplicated network were employed, the response curves would be moreirregular than those which are represented by the curves B and C, thatis, they would have a greater number of .peaks d valleys, and it willordinarily be desirable provide a network which will result in responsecurves which in this respect are more irregular than the curves B and C.v

The musical-result obtained by thus varying the response curve ofthe"output circuit periodically at a tremulant periodicity is sensedrather as an indefinable richness in the tone'than as an or-' dinarytremulant, which latter is usually perceived as a periodic change inamplitude.

lant.

As the impedance of one of the elements of the complicated network inthe output circuit is proaches that of a vibrato than that of atremuforming screen 24 of. the tube 23 isconnected to a source voltagedropping resistor R8 and resistor R8. The plate 25' of the tube 23 hasits output circuit resistance-coupled to the input circuit-of tube 26,

the first stage of the preamplifier, The

of plate potential indicated as +13 through a suitable blockingcondensers C2 and C3 being provided in th input circuit thereof. Thetube 26 forms the second sageof the preamplifier,

while the'output of the tube 26 is coupled with a power amplifier 28 bya transformer 30. The supplies one or more loud j power amplifier 28speakers 32.; v

Assuming a sustained signal of constant amplitude supplied to the inputterminals 26, 2l, the

tone produced by the loud speaker 32 would ,be-

J of constant quality and intensity, In accordance with the presentinvention, however, anadditional A circuit affecting the potential ofthe screen grid 24 of the tube 23 is provided.- This circuit, whenrendered effective, periodically changes the im-.

pedance of a circuit connecting the screen grid to ground, at atremulant rate, in the-order of This is due to the fact that the effectmore closely ap changed, the peaks of maximum. response shift fromfrequency to frequency, and'thus, if there is a wide range offrequencies present in the out:

put signal; the effect upon the ear will be that" of a frequencyshiftrather than a 'change in amplitude. Of course the changes take place atthe periodicity of the usual tremulant in theorder of 7 CI P. S. As aresult, there areso many changes in' amplitude, some frequenciesincreas-' ,ing and others decreasing, that the ear is unable to followth individual changes, butv instead,

hears the compositeeffect and perceives it more as a qualitative changein the tone'than as a change in amplitude.

The changes in the frequency response of the output circuit-may beaccomplished ina great The tremulant apparatus is connected to .the

screen 24 through a blocking condenser C6 which may have a 'value of.l-microfarads, throuh a conductor 34. The conductor 34 is connected toground through three parallel circuits, thefirst of which-comprisesavariable resistance 36 by means of whichthe degreeof effectiveness ofthe tremulant is controlled. This resistance may be in the order of0100,0'00 ohms, and'will, of

course, effestively ground the conductor 34 when it is adjusted to itsminimum resistance.

The secondof theparallel circuits connecting conductor 34 to groundincludes a condenser C9 which may have a value in the order of .0045

Y microfarads, and which is in series with a variable many different\ways by any one. of a nearly infinite variety of networks connected invarious ways in the output circuit of the instrument. The

, principles underlying the design of such networks are well understood,and since reference may be had to various texts on the subject, it isunnecessary herein to set forth these principles or to elaborate'uponthe various circuits in which the structural features of the inventionmay be resistance RT and a fixed resistance Rl6, which flatter may have.a value of approximately 1200,

ohms.

from zero to maximum value periodically at aftremulant rate in the orderof 6 or. '7 C..P'. S., and is diagrammatically illustrated, as'comprising aplurality of resistors 38 which are adapted to beprogressively connected in the circuit; and dis-,

The variable resistance RT ischanged connected therefrom, by a bus bar40 which is oscillated by a continuously rotating eccentric 42. Theeccentric 42 is driven through a suitable.

,spee'd reducing gearing from a -motor 44, the

embodied or by whichthe method of the invention may be performed. As aspecific example of one form in which the speed of which maybe-con'trolled by a variable resistance 46 inits power supply circuit;

' The third of the parallel circuits connecting the conductor-34 -toground includes an inductance 48 which may have a value in the order of250 henries. This inductance may, if desired, be ad "justable, althoughin most instances it will be i preferable to have it of fixed value.

invention may be embodied-reference may be had to the diagram of Figure2.

In Figure 2, the signal, usually composed of a plurality of differentfrequencies, upon which the tremulant is to be impressed,'is supplied toinput terminals 28, 2|. While the tremulant apparatus cal instruments,it is particularly designed for use in connection with electric organs,such as the type disclosed .in the aforesaid Patent No. 1,956,350; 1 Ther'elativelylow voltage signal-supplied by such instrument to the inputterminals 20, 2| of a preamplifier may be impressed upon the inputcircuit including the grid 22 of a pentode 23,

Assuming that a signal containing a large num-- ber of frequencies isimpressed upon the input terminals 20, 2l of the preamplifier, and thatthe 'maybe used for various types of electrical musivariable resistance36 is adjusted to an. intermediate value,.the tremulant resistance RT,as it is varied between its maximum and minimum values, will vary theeffective impedance of the circuit by which the'screen 24 of the tube23.is'

connected to ground. The inductance 48 is of such value that it willoffer very little impedance to the lowermost frequencies, and as aresult, the gain of the tube 23 will be at its maximum with respect tothe lower bass notes which will not be vary greatly afiected by thetremulant apparatus.

The choke 48, does, however, offer appreciable impedance to the higherfrequencies so that the musician.

latter ar modulated by the varying tremulant resistance RT, and apronounced tremulant is therefore impressed upon frequencies in thetreble register; The modulation is of course effected by the variationin gain of the amplifier tube will be low. It will bereadily apparentthat' by choosing an inductance 48 and a condenser C9 of proper values,the frequency response of the network, and hence of the amplifier as awhole, may be made'to follow substantially any desired pattern. Byutilizing a more complicated network, the frequency response of theapparatus may be made more irregular. The circuit may thus be made. toproduce results which appear to be most desirable from the point of viewof the While Ihave shown the condenser C9 connected in parallel with theinductance 48, it will be readily apparent to those skilled in the artthat the condenser C9 may be placed in series with the inductance 48instead of'in series with the tremulant resistor RT and resistance RIB.

, Using the circuit and apparatus shown in Figure 2, the frequencyresponse of the output circuit has been determined and found to followthe curves shown in Figure 1,.'the curve B- representing the responsewhen the tremulant contacts R'I' are open, while the'curve 0 representsthe response when the tremulant contacts are closed.

It will thus be seen that the relatively simple network of Figure 2produces comparatively regular response curves. Since to a certainextent it is desirable to have a frequency response represented bycurves -with a larger number of peaks and valleys than are found in thecurves B and C, it will be apparent that in most instances it will bedesirable to provide a more complicated network than that shown inFigure 2. Furthermore, the network may be associated with the outputcircuit in other-ways than in the screen circuit,

and itwill be apparent to those skilled in the art that the tremulantnetwork may, in the form in which it is shown, or in other forms, beassociated with other elements of the output circuit such as thesuppressor grid of one of the amplifying tubes, the control grid througha degenerative feedback circuit, or in connection with other The methodof my invention may therefore be performed by.

elements of the output circuit.

underlying principles of my invention. I therefore desire by thefollowing claims to include within the scope of my invention, all suchequivalent methods, apparatus, and circuits, whereby substantially theresults of my invention may be obtained in substantially the same way orby substantially the same means.

I claim:

1. In an electrical musical instrument inwhich the electrical signalsare amplified by a multielectrode electron discharge device having ascreen grid and translated into sound, means for producing a tremulanteflect comprising a network connecting said screen to apoint of fixedpotential, said network including inductive and capacitative reactances,and a variable resistance, and means for varying said resistance at atremulant periodicity.

2. The combination set forth in claim 1 in which said screen isconnected to said point of fixed potential by an additional manuallyadjustable variable resistance.

3. The combination set forth in claim 1 in which said network includestwo parallel circuits connecting said screen and said point of fixedpotential, one of said parallel circuits including a condenser and aperiodically varying resistance, and the other of said parallel circuitsincluding an inductance.

4. The combination set forth'in claim 1 in which said network includesthree parallel circuits connecting said screen grid to said point offixed potential, and in which the first of said parallel circuitsincludes a manually adjustable resistance, the second of said circuitsincludes a condenser and 'periodically varying resistance in series, andthe third of said circuits includes an inductance.

5. The combination set forth in claim 1 in which said network comprisesa periodically varying impedance of average value which is relativelyhigh for signals of high musical frequency, and a circuit shunting saidimpedance and including an inductance ofiering no appreciable impedanceto signals of low musical frequency.

6. In an electrical musical instrument in which the electrical signalsare amplified by a multielectrode electron discharge device having anelectrode the potential of which determines the degree of amplificationof the device, and in which the amplified signal is translated intosound, means for producing a tremulant efiect comprising, a networkconnecting said electrode to a point of fixed potential, said networkincluding inductive and capacitive reactances and a variable resistance,and means for varying said resistance at a tremulant periodicity.

MATTHEW Z. MIR-OZ.

